The present invention relates to an apparatus for detecting the in-focusing conditions used for an optical machinery such as cameras, microscopes, endoscopes and the like.
As one of the conventional apparatus for detecting the in-focusing conditions, photo-electro transducer elements such as CdS cell or the like are arranged in front and in the rear of a predetermined focal plane of an optical system, illuminance signals from these two elements are compared with each other and an in-focusing position is detected. In this apparatus, however, when the optical system is at the in-focusing position, it is necessary to make levels of these illuminance signals of two photo-electro transducer elements equal, so that it is difficult to arrange these two elements in correct position, and a precision is worse since the illuminance signals are compared at a fixed position. In case of changing a depth of a focus by modifying or exchanging an optical system, if the setting positions of two photo-electro transducer elements in front and in the rear of a predetermined focal plane are not changed accordingly, it is impossible to detect a precise in-focusing position.
There is another apparatus for detecting the in-focusing conditions which is so constructed that photo-electro transducer elements such as CdS cell or the like are arranged in front and in the rear of a predetermined focal plane in the same manner as described above, images focused on these two elements are scanned by a rotary mirror, contrasts of images on these elements are sought and compared with each other, thereby to detect an in-focusing position. Even in this apparatus, however, when the optical system is at the in-focusing position, it is necessary to arrange two elements so as to make respective contrasts of images on two photo-electro transducer elements equal to each other, so that it is also difficult to arrange these elements in correct position. This disadvantage also arises in case of changing depth of focus of the optical system. Moreover, in order to seek the contrasts, it is necessary to obtain an illuminance signal of a picture element array by scanning an image formed on a plane orthogonal to an optical axis at an arranged position to respective photo-electro transducer elements on the light receiving surfaces of respective elements, so that a rotary mirror for scanning and its driving device are required, and thus, an apparatus itself becomes disadvantageously large as a whole.
A further apparatus is also proposed which is so constructed that a light receiver consisting of image sensors such as CCD (charge coupled device) or the like is provided on a predetermined focal plane of an optical system, the magnitudes of contrasts for the images focused on the light receiver are compared with each other in succession thereby to detect the in-focusing conditions. In this apparatus, however, in successive comparison of the magnitudes of the contrasts, the in-focusing position is detected by the change of a polarity of the result obtained by the comparison, so that the detected position of the in-focusing does not meet with the actual in-focusing position of the optical system and thus the precision of the in-focusing detection becomes worse. In case of automatically moving and adjusting the optical system to an in-focusing position based on the result of comparison, even if the direction of the deviation of the in-focusing position is found by a polarity of the result of comparison, an amount of the deviation cannot be found, so that its control becomes complicated and troublesome, and its response becomes also a problem.